Roadways: Design Vehicle

Primary Guidance

Design Vehicle should be based on roadway functional classification and context Purpose and Need of the project should identify and specific needs for the project.
The maximum design vehicle for interstates shall be based on the largest vehicle allowed on Maryland roads without hauling permits

Discussion

Large design vehicles typically do not lead to significantly larger design criteria along mainline roadways. Geometric elements such as curb radii and pavement widths will be significantly larger based on a larger design vehicle.

The following is a list of the maximum design vehicle that should be considered based on the functional classification:

Interstate - WB-67 (large semi-trailer, 53 ft. trailer) The design vehicle should be considered for through movements as well as turning movements at all interchanges along interstate.

Freeway/Arterials – WB-62 (large semi-trailer, 48 ft. trailer) The design vehicle should be used on all State routes (excluding interstate).
If there is a state to state (MD and US Routes) intersection/interchange, turning movements should be designed to allow for a WB-62 to make all movements through the intersection/interchange. If truck volumes are high, wheel paths through the intersection should be paved.

Unless otherwise specified, adjacent public roadways connecting to a State route via an at-grade intersection should use a maximum design vehicle of a WB-50 for state route to county (or vice-versa) movement.

Commercial and Residential Access should be designed according to the vehicle(s) that will utilize the access. For example, an entrance to a farm is proposed off a State roadway. The design vehicle used may be a specific piece of farm equipment using the entrance.

For movements on State facilities that are unique, coordinate with the appropriate office or agency to determine the design vehicle turning paths. As an example, the MDOT’s Maryland Port Administration entrances may need to be designed for turning movements that exceed the vehicles that are listed above. The designer should coordinate with the specific MDOT TBU office to obtain vehicle specifications to ensure that turning movements are incorporated into the design.